1. Field of the Invention
The present invention relates to an elastomeric polyurethane gel composition which is suitable for use as an adhesive for nonwoven fibrous materials and a process for making this composition. The invention also relates to nonwoven fabrics made with these gel-forming reactants.
2. Description of the Prior Art
Polyurethane gel production is known. The Windemuth et al. U.S. Pat. No. 2,948,691 discloses that isocyanate modified polyglycolethers, especially those having a molecular weight higher than 2,000, are soluble in water. These polymers are prepared by reacting polyglycolethers having at least two terminal hydroxyl groups with either mono- or polyfunctional aliphatic or aromatic isocyanates. Aqueous solutions prepared with these materials are not stable because of the high reactivity of the isocyanate group in water. Thickening or gel formation is said to occur with increasing molecular weight within an interval of some minutes depending on the solid content of the solution.
For example, a solution of 4 percent of an isocyanate modified polyglycolether prepared from a polyglycolether of the molecular weight of 4,030, which is obtained by the addition of ethylene oxide to trimethylolpropane, produces a gelatinous mass. In another example an isocyanate modified polyglycolether containing 3.2 percent of NCO groups, was obtained from a polyglycolether based on the addition of ethylene oxide to trimethylolpropane and toluene diisocyanate. Upon stirring the product into water it solidified into an insoluble gel with the evolution of carbon dioxide which was perceived by the formation of bubbles in the gel, especially when large quantities of isocyanate are used. Windemuth discloses this gel-forming reaction as being adapted to the thickening of aqueous solutions or emulsions. Windemuth's reaction products of the polyglycolether and the isocyanate are summarized as being used for producing plasticizers, lubricants, plastics, spongy materials, gel formers, thickening agents, auxiliaries in textile industry and the like, with no teaching or suggestion of use as a nonwoven fiber adhesives.
In the Asao et al. U.S. Pat. No. 3,719,050 a polyurethane prepolymer having terminal isocyanate groups is reacted with water in the soil to gel the polyurethane prepolymer and solidify the soil. The elastomer formed is said to have excellent strength and to strongly adhere to the soil to improve the soil properties.
The polyurethane prepolymer of Asao et al is synthesized from 2 to 8 moles of polyisocyanate per mole of a polyalkylene oxide compound. The alkylene oxides employed include ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO), as well as styrene oxide and epichlorohydrin. In preferred embodiments the prepolymer is obtained as a reaction product of an ethylene oxide-propylene oxide copolymer having an ethylene oxide unit and propylene oxide unit in a ratio of from 90/10 to 70/30, which is reacted with an isocyanate compound having at least two isocyanate groups.
The polyurethane prepolymer is liquid or pasty at room temperature, and when added to 97 to 85 percent by weight of water, it readily dissolves, thereby forming a transparent solution, or is dispersed homogeneously therein to form an emulsion. The aqueous solution or emulsion is converted in a period of 20 seconds to two hours to a water-insoluble water-containing plastic material having a high elasticity. The polymerization of the urethane prepolymer by the cross-linking reaction with water produces carbon dioxide. Since the carbon dioxide gas produced is dissolved in the water present in the system, the resultant water-containing plastic material is a gel with a slight increase in volume owing to the gas formation.
The only utility of this polyurethane prepolymer is to form a gel when used as a soil-injecting agent. Inorganic materials such as clay, cement and the like can be mixed with the prepolymer and then injected into the soil. The elastomer which forms is said to have an extremely excellent strength and it markedly improves the soil in view of its strong adherence to the soil.
The Harada et al. Pat. No. 4,118,354 discloses a similar gel produced by dispersing a reaction product obtained by the reaction of a polyisocyanate having at least two isocyanate groups with a polyether. The polyether comprises a plurality of alkylene oxides, 50 to 90 percent by weight of which is ethylene oxide, added at random to a polyalcohol having at least two terminal hydroxyl groups. The alkylene oxides are added in an amount of an average molecular weight within the range of 1,000 to 4,000 per each hydroxyl terminal group of the polyalochol.
The disclosed utility of these gels is in disposing of various sludges of the bottom of rivers, seas, and sludges removed from organic and inorganic waste liquids and sewage. The polyurethane hydrogels are also employed in disposing of liquid wastes released from breweries, papermills, dye works, tanneries, slaughter houses, etc. Further, aqueous solutions containing noxious metals and radioactive substances are said to be effectively confined within the polyurethane hydrogel to prevent them from being scattered.
The Wood et al. U.S. Pat. No. 4,246,146 discloses a generic class of elastomeric polyurethane gel compositions which includes the preferred materials of this invention. However, these compositions are mixed with large quantities of fire retardant materials to form a coating which provides a barrier for fire retardant protection.
In each of the Windemuth et al., Asao et al., Harada et al. and Wood et al. patent references, there is no discussion of making their gel compositions with aliphatic isocyanates to obtain an adhesive for binding nonwoven fabrics.